Many drugs, such as sodium thiopental, marketed under the trademark Sodium Pentothal, are stored in powdered lyophilized form and mixed with a liquid, such, as sterile water or normal saline immediately prior to use. This is necessary to maintain the stability and potency of such drugs.
The concept of mixing wet and dry components within the barrel of a syringe or vial has been known in the past. Much of the mixing has been done within glass vials, some of which have had dislodgable central barriers, such as U.S. Pat. No. 2,660,171. Mixing within the vial was a tedious process involving swishing and swirling and took considerable time.
Another type mixing syringe that had this same problem of slowly dissolving both components in a single compartment after the components were combined is described in the Ogle U.S. Pat. No. 3,397,694. In this patent, a liquid-containing vial has a piston for pressure injection of a liquid into the syringe barrel containing the dry powder. The powder can then slowly dissolved in the liquid entirely within the syringe barrel. The vial piston is shown as a very thick solid mass of rubber material, and would have a high frictional drag on the vial wall to seal it against the high pressures exerted on the stopper to puncture out the barrier system, as described in this patent. Because of such high frictional drag between the piston and vial, the piston is moved through only a one-time injection stroke, such as by thumb pressure (FIG. 5). Such thumb pressure would be unnecessary if the vial stopper were of low friction and trackable with retraction of the syringe plunger and stopper. As described, the device of this patent requires a manipulation first at the vial end, i.e. twisting or pushing, and then manipulation at the opposite end for pushing the syringe plunger for injection.
A similar wet-dry mixing syringe that included the problem mentioned above, i.e. tedious manipulation of opposite ends of the device, and shaking the combined components until the powder dissolved, was recently marketed by Abbott Laboratories under the name of "PENTOTHAL Ready-to-Mix Syringe." An undated instruction for its use is submitted with this application as background illustrating the problems mentioned in the Ogle Pat. No. 3,397,694. Since it is not known whether this Abbott syringe has been publicly available or on sale for more than a year, it is not submitted as prior art to applicants' invention, but only as a procedural illustration of the use of such devices of the type described in Ogle's U.S. Pat. No. 3,397,694.
While the above wet-dry mixing devices have accomplished the dissolving step in a single compartment, there has been a proposal to speed up such dissolving by a structure that couples two flexible containers similar in construction to toothpaste tubes together as shown in the Lockhart U.S. Pat. No. 2,724,383. As shown in FIGS. 8-10, the operator squeezes first one collapsible tube and then the other in a milking action to promote mixing. This is a tedious process because it requires substantial manual dexterity and sequential squeezing of alternate tubes in rapid succession.